1. Field of the Invention
The present invention refers to iterative localization techniques with wireless communication systems for rural environment with limited number of base stations in the range of the mobile station and urban environment with multipath propagation channel and several base stations in the range of mobile station.
2. Description of the Related Art
Localization awareness becomes an important system functionality of existing and emerging wireless communication systems in order to provide location based services, such as location based advertisements, location based social networking such as Facebook, MySpace, i.e. and for emergency to rescue of people (U.S. Pat. No. 6,404,388). On the other hand, the localization awareness is important additional system functionality for wireless network providers to improve their networks applying adaptive methods for network reconfiguration according to the instant spatial distribution of the users and verify the coverage prediction obtained by coverage prediction software tools. The localization methods have been reported in several previous works and they can be generally classified into three main groups, namely (i) methods based on angle of arrival (AOA), (ii) method based on time of arrival (TAO) for example in U.S. Pat. No. 6,459,903, (iii) methods based on time difference of the arrival (TDOA), (iv) received signal strength (RSS) techniques and finally (v) combination of mentioned techniques, for example as proposed in (U.S. Pat. No. 6,515,623).
Generally, with some exceptions, the proposed methods does not consider the limitations of the particular communication system such as, (i) does mobile station estimate the TOA of one or more base stations, (ii) does mobile station measure RSS of one or more base stations, (iii) does mobile station measure the DTOA, and the most important does mobile station send the measured data to the location server located somewhere on the network.
In addition, the available location base methods relay on the assumptions that the base station receives signal from more than two base stations, which may be true in dense populate urban environment fully covered by wireless networks. However, in a rural environment, in many cases the mobile terminal receives two or less base stations. The usage of the classical localization method in the circumstance is not possible, so for the usage of location services in rural area a new innovative methods are necessary, specially invented for a particular communication system, for example WiMAX, GSM, LTE, etc. In addition to mentioned drawbacks the majority of available methods, in particular those based on TOA, AOA and TDOA, assume line of sight propagation between transmitter and receiver, which is not true at all especially in urban and indoor propagation environment, where the radio propagation is mainly characterized by: reflection, refraction and diffraction. If in the multipath propagation environment several base stations are observed by mobile terminal, the mobile terminal, in order to increase the accuracy of the position calculation, have to select those base stations, which channel characteristic is close to line of sight channel. Though the channel estimation is implemented in nearly all mobile wireless communication systems, only RSS and time difference between serving and neighboring base stations is reported to the localization server, which limits the use of well known localization methods.
Thus there exists a need for new localization techniques for emerging communication system for rural environment with limited number of base stations in the range of the mobile station and urban environment with multipath propagation channel and several base stations in the range of mobile station. At the moment, there are two communication systems foreseen for next generation of the mobile communication systems, namely LTE and WiMAX. While the LTE is in its infancy several mobile WiMAX products are successfully installed in some countries also in remote rural areas. Therefore there exists a huge need for new localization methods, which do not require any changes in radio WiMAX protocol but on other hand finds location of the mobile WiMAX terminal in a rural or urban area when at least two base stations are in range of mobile stations.
A WiMAX standard specifies procedures for network topology acquisition which also includes the MS scanning of the neighbor base stations that is primarily applied for handover procedure. However, the data from the scanning procedure can be applied also for estimation of the mobile station location. The scanning procedure starts with MOB-SCN-RSP message sent from serving base station to the mobile station defining the scanning interval. The BS responds with the MOB-SCN-REP message which among other includes (i) the CINR measured by the MS from the particular BS with the resolution of 0.5 dB, (ii) Received Signal Strength Indicator (RSSI) measured by the MS from the particular BS with the resolution of 0.25 dB in the range from −103.75 dBm to the −40 dB, (iii) relative delay which denotes the delay of neighbor DL signals relative to the serving BS measured by the MS for the particular BS, which value is expressed as a signed integer in units of samples and (iv) round trip delay (RTD) measured by the MS from the serving BS expressed and measured in resolution of 1/sampling frequency. The sampling frequency is function of the bandwidth given as floor (sampling factor*bandwidth/8000)*8000, where sampling factor depending on bandwidth can be 8/7 or 28/25. For example, the sampling frequency for the bandwidth equal to 10 MHz, the sampling frequency is equal 11.2 MHz. The data from the MOB-SCN-REP message can be forwarded through ASN server to the location server, where the location of the base station can be calculated by proposed invention.